The present invention is directed to control of defrost operations for refrigeration systems, including electrically operated heat pump systems, and especially to controlling scheduled defrost operations for a refrigeration system or an electrically operated heat pump system.
Many commercial refrigeration systems employ electro-mechanical relay timed control devices to schedule the start and control the termination of evaporator coil defrost operations. Many electrically operated heat pumps use similar timed control devices to defrost a heat exchanger outside of an air conditioned space when the heat pump is in a heating mode. For purposes of this disclosure the term “refrigeration systems” also is intended to include electrically operated heat pumps which use electric resistance heaters, microwave energy, or another electrically generated heat source to defrost a heat exchanger outside of an air conditioned space when operating in a heating mode. The timed control devices may be configured to be programmed to initiate a defrost operation at varied and multiple times throughout a day. The timing for defrost operations is typically specified by the needs of the application in which the particular refrigeration system is employed and by knowledge of the manufacturer or installer of the refrigeration system. The timed control devices may control the termination of a defrost process either upon receiving a signal from a temperature or pressure sensing device or upon lapsing of a maximum allowed time that may be pre-programmed in the timed control device. Once programmed, the timed control devices will typically activate the defrost operation in a consistent and repeating manner, regardless of the actual condition of the evaporator coil.
The manufacturer or installer must choose the appropriate number of defrosts, and the maximum allowed time for each defrost based upon knowledge of the application and type of equipment being used. Such design choices are sometimes based upon a worst-case scenario that the refrigeration system may be expected to encounter on a day-to-day basis. As a result of such a loose predictive selection method, the refrigeration system may defrost itself more times than is necessary on days not presenting the predicted worst-case scenario. Resulting additional defrosts in such environments are typically a waste of energy, and thus a waste of money. In addition, such additional defrost operations may put refrigerated products at risk of spoilage.
Redesigning a defrost control device for a refrigeration system may be expensive, especially in the case of already installed refrigeration systems.
There is a need for a defrost control method and apparatus that can be added to an existing refrigeration system to achieve control of defrost operations for a refrigeration system that is responsive to contemporaneous conditions rather than responsive to predicted environmental conditions.
There is a need for a method and apparatus for affecting defrost operations for a refrigeration system that is capable of analysis of performance of a refrigeration system and using results of the analysis to truncate a scheduled defrost operation when the method or apparatus determines that the defrost cycle is not required.